1. Field of the Invention
The present invention relates to an inkjet printing apparatus for carrying out printing by ejecting ink on a recording medium, such as a paper sheet.
2. Description of the Related Art
It is conventionally known with inkjet printing apparatuses that, in order to correct for deformed posture of a paper sheet, such as curl or cockling, a number of through holes for generating a suction force are formed in the surface of a platen, and a porous platen belt is provided to slide over the platen to suction and convey the paper sheet with the suction force generated at belt holes.
Japanese Unexamined Patent Publication No. 2007-152644 (hereinafter, Patent Document 1) has proposed an inkjet printing apparatus, wherein a distance between the upper surface of the platen belt and inkjet nozzles provided in the lower surface of an inkjet head (which will hereinafter be referred to as a head gap) is adjusted depending on the thickness of the paper sheet, thereby preventing the paper sheet being suctioned and conveyed by the platen belt from contacting the nozzle surface of the inkjet head and to prevent occurrence of jam caused by the contact between the paper sheet and the nozzle surface of the inkjet head.
In the above-described inkjet printing apparatus, when the belt holes which are not closed with the paper sheet pass above the through holes of the platen, the air above the platen belt is drawn into a space below the platen via the belt holes and the through holes, and streams of air are generated above the platen belt. The range where the streams of air are generated is wider when the head gap is larger, and this may result in disturbed streams of air above the platen belt.
If such disturbed streams of air are generated in the vicinity of the inkjet nozzles, fine ink droplets (which will hereinafter be referred to as “ink mist”), which are formed when the ink is ejected, may be scattered, and the scattered ink mist may adhere on the paper sheet and/or the interior of the apparatus, which results in degradation of printing quality and contamination of the interior of the apparatus.